Steering control system for harvester and methods of using the same

ABSTRACT

The disclosure relates to a steering control system useful for providing stable control during high-speed operation of harvesters, such as self-propelled windrowers. The steering control system utilizes a sensor for detecting and regulating a position of a single steering cylinder associated with a first caster, a damper being free of sensing and providing passive damping to the second caster.

BACKGROUND

Harvesters such as windrowers, tractors, and forage harvesters, have tooperate effectively in different operational modes (e.g., normaloperation mode, in-field operation mode, high-speed operation mode, orthe like). Typical construction for such vehicles include front groundwheels mounted on the frame at fixed angles parallel to each other andparallel to a center line of the frame and rear ground wheels mounted ona respective caster. Each of the front ground wheels is typically drivenby a respective drive motor which allows variable speed in both theforward and reverse directions such that steering of the tractor iseffected by a differential in speed between the front wheels with therear wheels following the steering in a castering action.

Conventional harvesters generally use dual path steering for bothin-field operation mode and high-speed road transport operation mode.Dual path steering generally operates by varying the speed of the twofront drive wheels in order to steer the harvester. The left wheel slowswhile the right wheel speeds up to turn left, while the right wheelslows and the left wheel speeds up to turn right. Combined withpassively castering rear wheels, this enables the conventional harvesterto perform zero radius spin turns in the field, which is desirable foroptimum field efficiency and maneuverability. However, during high-speedroad transport operation mode (e.g., speeds greater than 24 mph) dualpath steering does not provide adequate steering stability. This is dueto several factors, including variable ground drive motor/pumpefficiency, lack of steering feedback to the driver, dynamics of theharvester which uses the front wheels to steer with no stabilizingeffect provided by the rear wheels, combinations thereof, or the like.

SUMMARY

The disclosure relates to a steering control system for a harvester thatprovides for stable operation during high-speed rear axle steering(e.g., road operation mode). The steering control system includes aposition sensor detecting the position of a single steering cylinderassociated with one caster of the windrower. Based on input from asteering wheel or device, the steering cylinder is actuated to extend orretract to steer one caster of the windrower, with the second casterproviding passive damping. In some embodiments, steering cylinders areprovided on both casters with the position of only one steering cylinderdetected by a sensor. In such embodiments, actuation of a first steeringcylinder to extend or retract results in an equal and opposite actuationof the second steering cylinder, thereby providing steering on bothcasters. Steering of one or both casters provides additional stabilityto the windrower during the road operation mode.

In accordance with some embodiments of the present disclosure, anexemplary steering control system for a harvester is provided. Thesteering control system includes a first cylinder configured to becoupled to a rear axle of the harvester at one end and an upright shaftof a first caster of the harvester at an opposing end. The steeringcontrol system includes a sensor associated with the first cylinder andin communication with a controller, the sensor detecting a position ofthe first cylinder. The steering control system includes a passivedamper configured to be coupled to the rear axle of the harvester at oneend and an upright shaft of a second caster of the harvester at anopposing end. In a road operation mode, the first cylinder is actuatedby the controller to extend or retract to control steering of the firstcaster, and the sensor transmits data to the controller regarding thedetected position of the first cylinder. The passive damper is free ofsensing and provides passive damping to the second caster.

One end of the first cylinder is configured to be coupled to the rearaxle of the harvester by a flange. In some embodiments, the firstcylinder is hydraulically plumbed to a steering proportional valve foractuation of the first cylinder to extend or retract. The steeringproportional valve is hydraulically plumbed to both a rod end and abarrel end of the first cylinder. The detected position of the firstcylinder is representative of a position of the first caster relative tothe rear axle of the harvester.

In some embodiments, the steering control system includes a proximitysensor configured to detect a position of the first caster relative tothe rear axle of the harvester. Castering of second caster is unaffectedby actuation of the first cylinder to extend or retract. In someembodiments, the sensor is at least one of an internal position sensor,an external position sensor, a potentiometer, or the like. In a fieldoperation mode, free flow of hydraulic fluid into and out of the firstcylinder provides passive damping by the first cylinder to the firstcaster.

In accordance with embodiments of the present disclosure, an exemplarysteering control system for a harvester is provided. The steeringcontrol system includes a first cylinder configured to be coupled to arear axle of the harvester at one end and an upright shaft of a firstcaster of the harvester at an opposing end. The steering control systemincludes a sensor associated with the first cylinder and incommunication with a controller, the sensor detecting a position of thefirst cylinder. The steering control system includes a second cylinderconfigured to be coupled to the rear axle of the harvester at one endand an upright shaft of a second caster of the harvester at an opposingend. In a road operation mode, the first cylinder is actuated by thecontroller to extend or retract to control steering of the first caster,and the sensor transmits data to the controller regarding the detectedposition of the first cylinder. The second cylinder is free of sensingand is hydraulically coupled to the first cylinder to move in an equaland opposite direction of the first cylinder to control steering of thesecond caster.

In some embodiments, barrel ports of the first and second cylinders arehydraulically coupled together, and rod ports of the first and secondcylinders are hydraulically coupled to a steering proportional valve.Actuation of the first cylinder to retract displaces fluid from a barrelend of the first cylinder into a barrel end of the second cylinder.Displacement of the fluid into the barrel end of the second cylinderactuates the second cylinder to extend in an equal magnitude toretraction of the first cylinder.

In some embodiments, the detected position of the first cylinder isrepresentative of a position of the first and second casters relative tothe rear axle of the harvester. In some embodiments, the steeringcontrol system includes a proximity sensor configured to detect aposition of the first caster or second caster relative to the rear axleof the harvester. In some embodiments, the sensor is at least one of aninternal position sensor, an external position sensor, a potentiometer,or the like. In a field operation mode, free flow of hydraulic fluidinto and out of the first and second cylinders provides passive dampingby the first cylinder to the first caster and the second cylinder to thesecond caster.

In accordance with embodiments of the present disclosure, an exemplaryharvester is provided. The harvester includes a frame, at least onefront axle comprising first and second front wheels pivotally mounted tothe front axle, at least one rear axle comprising first and secondcasters pivotally mounted to the rear axle, and a steering controlsystem. The steering control system includes a first cylinder coupled tothe rear axle at one end and an upright shaft of the first caster at anopposing end. The steering control system includes a sensor associatedwith the first cylinder and in communication with a controller, thesensor detecting a position of the first cylinder. The steering controlsystem includes a passive damper coupled to the rear axle at one end andan upright shaft of the second caster at an opposing end. In a roadoperation mode, the first cylinder is actuated by the controller toextend or retract to control steering of the first caster, and thesensor transmits data to the controller regarding the detected positionof the first cylinder. The passive damper is free of sensing andprovides passive damping to the second caster. Castering of secondcaster is unaffected by actuation of the first cylinder to extend orretract.

In accordance with embodiments of the present disclosure, an exemplaryharvester is provided. The harvester includes a frame, at least onefront axle comprising first and second front wheels pivotally mounted tothe front axle, at least one rear axle comprising first and secondcasters pivotally mounted to the rear axle, and a steering controlsystem. The steering control system includes a first cylinder coupled tothe rear axle at one end and an upright shaft of the first caster at anopposing end. The steering control system includes a sensor associatedwith the first cylinder and in communication with a controller, thesensor detecting a position of the first cylinder. The steering controlsystem includes a second cylinder coupled to the rear axle at one endand an upright shaft of the second caster at an opposing end. In a roadoperation mode, the first cylinder is actuated by the controller toextend or retract to control steering of the first caster, and thesensor transmits data to the controller regarding the detected positionof the first cylinder. The second cylinder is free of sensing and ishydraulically coupled to the first cylinder to move in an equal andopposite direction of the first cylinder to control steering of thesecond caster.

In accordance with embodiments of the present disclosure, an exemplarymethod of steering a harvester is provided. The method includes couplinga first cylinder to a rear axle of the harvester at one end and anupright shaft of a first caster of the harvester at an opposing end. Themethod includes associating a sensor with the first cylinder, the sensorin communication with a controller and detecting a position of the firstcylinder. The method includes coupling a passive damper to the rear axleof the harvester at one end and an upright shaft of a second caster ofthe harvester at an opposing end, the passive damper being free ofsensing. In a road operation mode, the method includes actuating thefirst cylinder by the controller to extend or retract to controlsteering of the first caster, and transmitting data to the controllerregarding the detected position of the first cylinder. The methodincludes providing passive damping to the second caster with the passivedamper.

Any combination and/or permutation of embodiments is envisioned. Otherobjects and features will become apparent from the following detaileddescription considered in conjunction with the accompanying drawings. Itis to be understood, however, that the drawings are designed as anillustration only and not as a definition of the limits of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of skill in the art in making and using the disclosedsteering control systems, reference is made to the accompanying figures,wherein:

FIG. 1 is a perspective view of a windrower with an exemplary steeringcontrol system of the present disclosure;

FIG. 2 is a perspective view of a windrower with an exemplary steeringcontrol system of the present disclosure;

FIG. 3 is a perspective view of a rear axle of a windrower with anexemplary steering control system of the present disclosure;

FIG. 4 is a detailed view of a steering assembly of an exemplarysteering control system of the present disclosure;

FIG. 5 is a detailed view of a damping assembly of an exemplary steeringcontrol system of the present disclosure;

FIG. 6 is a top view of an exemplary steering control system of thepresent disclosure in a left turn operation;

FIG. 7 is a top view of an exemplary steering control system of thepresent disclosure in a right turn operation;

FIG. 8 is a detailed view of a steering assembly of an exemplarysteering control system of the present disclosure;

FIG. 9 is a static image of a hydraulic circuit of an exemplary steeringcontrol system of the present disclosure;

FIG. 10 is the hydraulic circuit of FIG. 9 in a field operation mode;

FIG. 11 is the hydraulic circuit of FIG. 9 in a straight path operationmode;

FIG. 12 is the hydraulic circuit of FIG. 9 in a right turn operationmode;

FIG. 13 is the hydraulic circuit of FIG. 9 in a left turn operationmode;

FIG. 14 is a perspective view of an exemplary steering control system ofthe present disclosure;

FIG. 15 is a detailed view of an exemplary steering control system ofthe present disclosure;

FIG. 16 is a detailed view of an exemplary steering control system ofthe present disclosure;

FIG. 17 is a top view of an exemplary steering control system of thepresent disclosure in a left turn operation;

FIG. 18 is a top view of an exemplary steering control system of thepresent disclosure in a right turn operation;

FIG. 19 is a static image of a hydraulic circuit of an exemplarysteering control system of the present disclosure;

FIG. 20 is the hydraulic circuit of FIG. 19 in a field operation mode;

FIG. 21 is the hydraulic circuit of FIG. 19 in a straight path operationmode;

FIG. 22 is the hydraulic circuit of FIG. 19 in a right turn operationmode;

FIG. 23 is the hydraulic circuit of FIG. 19 in a left turn operationmode; and

FIG. 24 is a static image of a hydraulic circuit of an exemplarysteering control system of the present disclosure.

DETAILED DESCRIPTION

Various terms relating to the methods and other aspects of the presentdisclosure are used throughout the specification and claims. Such termsare to be given their ordinary meaning in the art unless otherwiseindicated. Other specifically defined terms are to be construed in amanner consistent with the definition provided herein.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise.

The term “more than 2” as used herein is defined as any whole integergreater than the number two, e.g., 3, 4, or 5.

The term “plurality” as used herein is defined as any amount or numbergreater or more than 1. In some embodiments, the term “plurality” means2, 3, 4, 5, 6 or more.

The terms “left” or “right” are used herein as a matter of mereconvenience, and are determined by standing at the rear of the machinefacing in its normal direction of travel. Likewise, “forward” and“rearward” are determined by the normal direction of travel. “Upward”and “downward” orientations are relative to the ground or operatingsurface as are any references to “horizontal” or “vertical” planes.

The term “about” as used herein when referring to a measurable valuesuch as an amount, a temporal duration, and the like, is meant toencompass variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, ±0.4%, ±0.3%,±0.2%, ±0.1%, ±0.09%, ±0.08%, ±0.07%, ±0.06%, ±0.05%, ±0.04%, ±0.03%,±0.02% or ±0.01% from the specified value, as such variations areappropriate to perform the disclosed methods.

The term “harvester” as used herein is defined as a machine thatconsolidates and/or packages material so as to facilitate the storageand handling of the material for later use. In some embodiments, theharvester is used to harvest agricultural material. In some embodiments,the harvester is a windrower, a forage harvester, lawn mower or acombine including a baling mechanism. In some embodiments, the harvesteris a self-propelled windrower.

The term “material” as used herein is defined as a numerous individualitems that are harvested or collected by the harvester. In someembodiments, the material is agricultural crop, such as hay or silage.In some embodiments, the material is biomass.

The term “drive system” or “steering system” as used herein is definedas an assembly, hydraulic or mechanical arrangement that allows forcontrol of the front and/or rear wheels of the harvester.

The term “information” as used herein is defined as data valuesattributed to parameters. In some embodiments, information is digitaland/or analog information. In some embodiments, information is thecurrent operable mode of the harvester. In some embodiments, warninginformation can be audio and/or visual information. In some embodiments,warning information is information that is capable of alerting anoperator that an action may need to be taken.

Discussions herein utilizing terms such as, for example, “processing,”“computing,” “calculating,” “determining,” or the like, may refer tooperation(s) and/or process(es) of a computer, a computing platform, acomputing system, or other electronic computing device, that manipulateand/or transform data represented as physical (e.g., electronic)quantities within the computer's registers and/or memories into otherdata similarly represented as physical quantities within the computer'sregisters and/or memories or other information storage medium that maystore instructions to perform operations and/or processes.

Some embodiments may take the form of an entirely hardware embodiment,an entirely software embodiment, or an embodiment including bothhardware and software elements. Some embodiments may be implemented insoftware, which includes but is not limited to firmware, residentsoftware, microcode, or the like.

Furthermore, some embodiments may take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For example, a computer-usable orcomputer-readable medium may be or may include any apparatus that cancontain, store, communicate, propagate, or transport the program for useby or in connection with the instruction execution system, or harvester.In some embodiments, the harvester includes a software system withexecutable code that executes different hydraulic states based onoperator steering of the harvester. In some embodiments, the disclosurealso relates to a computer software product with executable code thatautomatically toggles between or through different hydraulic statesbased on operator steering of the harvester. The software programproduct may be on any medium or a component of a system optionallyconfigured for update or install into the software of an existingharvester.

In some embodiments, the medium may be or may include an electronic,magnetic, optical, electromagnetic, InfraRed (IR), or semiconductorsystem (or apparatus or device) or a propagation medium. Somedemonstrative examples of a computer-readable medium may include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a Random Access Memory (RAM), a Read-Only Memory (ROM), arigid magnetic disk, an optical disk, or the like. Some demonstrativeexamples of optical disks include Compact Disk-Read-Only Memory(CD-ROM), Compact Disk-Read/Write (CD-R/W), DVD, or the like.

In some embodiments, the disclosure relates to a processing systemincluding a processing device suitable for storing and/or executingprogram code and may include at least one processor coupled directly orindirectly to memory elements, for example, through a system bus. Thememory elements may include, for example, local memory employed duringactual execution of the program code, bulk storage, and cache memorieswhich may provide temporary storage of at least some program code inorder to reduce the number of times code must be retrieved from bulkstorage during execution. In some embodiments, the memory is capable ofstoring preferred settings or information about steering of theharvester. In some embodiments, the system includes one or a pluralityof sensors to detect the steering selected by the operator. The sensorsmay be hard wired to one or more wires creating a physical connection toone or a plurality of controllers and/or are active sensors can beactivated and used over a WiFi hotspot, Bluetooth® or other internetconnection with controllers capable of receiving such remote signals.

In some embodiments, input/output or I/O devices (including but notlimited to keyboards, displays, pointing devices, etc.) may be coupledto the system either directly or through intervening I/O controllers. Insome embodiments, I/O devices may be coupled to the system directly orto I/O controller by an I/O bus (cables and or wires which connect thedevices and enable the information to pass therebetween). In someembodiments, network adapters may be coupled to the system to enable thedata processing system to become coupled to other data processingsystems or remote printers or storage devices, for example, throughintervening private or public networks. In some embodiments, modems,cable modems and Ethernet cards are demonstrative examples of types ofnetwork adapters. Other suitable components may be used. Any sensordisclosed herein may function on any disclosed harvester by integrationinto one or more data processing systems of the harvester. For example,in some embodiments, the disclosure relates to a data processing systemincluding executable software program product configured for sending andreceiving information about the steering of the harvester. In someembodiments, the system may be configured by the operator to transitionthe harvester between different hydraulic states in synchrony orsubstantial synchrony to operator-initiated steering of the harvester.In some embodiments, the data processing system of the harvestertransitions the harvester between different hydraulic states insynchrony or substantial synchrony to operator-initiated steering of theharvester depending upon real-time information sent to a controller by asensor that monitors the steering wheel actuation.

The term “real-time” and the phrase “in real-time” as used herein aredefined as a way of describing a process, event, or action that occurssimultaneously with the process of actively operating a harvester. Insome embodiments, various sensors continuously sense information aboutthe steering operation of the harvester and transmit that information toa controller in real-time. In some embodiments, an operator may adjustvalues or thresholds for one or more hydraulic states in real-timethrough the operator interface by accessing the system electronicallyand inputting one or a plurality of values.

Many of the fastening, connection, processes and other means andcomponents utilized in this disclosure are widely known and used in thefield of the disclosure described, and their exact nature or type is notnecessary for an understanding and use of the disclosure by a personskilled in the art, and they will not therefore be discussed insignificant detail. Furthermore, the various components shown ordescribed herein for any specific application of this disclosure can bevaried and the practice of a specific application of any element mayalready be widely known or used in the art by persons skilled in the artand each will likewise not therefore be discussed in significant detail.

Windrowers and tractors, such as self-propelled windrowers, are wellknown in the agricultural industry, and the instant invention can beused with substantially any of such machines. Reference is made, forexample, to U.S. Pat. Nos. 9,101,090 and 8,020,648; that illustrate suchwindrowers, the disclosures of which are incorporated herein byreference in their entireties. Embodiments of the present invention areparticularly well suited, but in no way limited to, use with windrowers.The present invention may also find utility in agricultural harvestersincluding, for example, a self-propelled windrower, a forage harvester,cotton harvester or a lawn mower. Embodiments of the present disclosureare particularly well suited, but in no way limited to, use with anyvehicle with a front and rear steer system.

In some embodiments, the method is performed by a harvester comprising acrop supply chamber, a crop gating system, and one or more sensors. Insome embodiments, the one or more sensors are capable of determining arange of information, including, but not limited to, one or acombination of: the size of a bale in the bale chamber (diameter and/orweight), the position of the tailgate, the position of the control arm,the position of the rear wall, and the position of the crop gatingsystem. In some embodiments, the one or more sensors are in electroniccommunication with one or more controllers. In some embodiments, sensorscan be used to determine that the caster cylinders are fully retractedor extended.

FIG. 1 shows a perspective view of an exemplary windrower 100. Thewindrower 100 generally includes front wheels 102, 104 rotatably mountedto a frame 106. The windrower 100 includes a cabin 108 mounted to theframe 106. The cabin 108 is configured and dimensioned to receive anoperator, and has a plurality of controls for operation of the windrower100, such as controlling a header 110 attachable to the front 112 of thewindrower 100, controlling movement of the windrower in a forwarddirection 114, and controlling movement of the windrower 100 in areverse direction 116.

At the rear 118, the windrower 100 includes casters 120, 122 rotatablymounted on opposing sides of a rear axle 124 of the frame 106. Thewindrower 100 includes two independent caster wheels 126, 128 mounted tothe respective casters 120, 122, one on the left-hand side and one onthe right-hand side of the windrower 100. The windrower includes asteering control system 130 including a damping assembly 132 (e.g., apassive damper, shock absorbers, or the like) and a steering assembly134 (e.g., a hydraulic steering cylinder) mounted to the frame 106. Aswill be discussed in greater detail below, the damping assembly 132provides damping functionality to one of the casters 120, 122, and thesteering control system 130 provides steering functionality to the othercaster 120, 122. As such, only one of the casters 120, 122 is damped andthe other caster 120, 122 is steered. Although illustrated as located onthe left-hand and right-hand sides, it should be understood that theposition of the damping and steering assemblies 132, 134 could bereversed.

FIGS. 2 and 3 show perspective views of the windrower 100 and rear axle124 of the windrower with the steering control system 130. FIGS. 4 and 5show detailed views of the steering and damping assemblies 134, 132 ofthe steering control system 130. The damping assembly 132 includes apassive damper 136 (e.g., a shock absorber, a shimmy damper, or thelike) pivotably coupled at one end to an arm 138 and pivotably coupledat the opposing end to a flange 140. The damper 136 passively damps theoscillation of the caster 120 without providing any steering action ofthe caster 120. The opposing end of the arm 138 is rigidly coupled tothe top of an upright shaft 142 and is rotatable about a pivot axisdefined by the upright shaft 142 (e.g., the pivot axis of the caster120) with the caster 120. The shaft 142 and the arm 138 thereby rotatetogether with the caster 120. The opposing end of the flange 140 isfixedly coupled to the axle 124 and does not pivot. The upright shaft142 pivots within the axle 124 with the flange 140 remaining in a fixed,rigidly mounted position on the axle 124. The rigid position of theflange 140 allows for the extension and retraction of the damper 136 asthe assembly of the arm 138, the shaft 142, and the caster 120 rotatesabout the axis of the shaft 142. The extension and retraction of thedamper 136, in turn, provides damping to the caster 120.

The steering assembly 134 includes a steering cylinder 144 (e.g., ahydraulic cylinder) pivotably coupled at one end to an arm 146 andpivotably coupled at the opposing end to a flange 148. The cylinder 144can be hydraulically actuated to extend or retract, thereby providingsteering to the left-hand side caster 122. The opposing end of the arm146 is rigidly coupled to the top of an upright shaft 150 and isrotatable about a pivot axis defined by the upright shaft 150 (e.g., thepivot axis of the caster 122) with the caster 122. The shaft 150 and thearm 146 thereby rotate together with the caster 122. The opposing end ofthe flange 148 is fixedly coupled to the axle 124 and does not rotatewith the shaft 150. The arm 146 is rigidly coupled to the shaft 150,with the shaft 150 rigidly connected to the caster 122. The arm 146, theshaft 150, and the caster 122 thereby rotate within the upright of axle124 about the axis of the shaft 150. The steering assembly 134 includesone or more sensors 152 capable of detecting the position or amount ofextension/retraction of the cylinder 144, and transmits datacorresponding to the position of the cylinder 144 to a controller module154 as feedback regarding steering of the caster 122.

Hydraulic lines 156, 158 (e.g., pressure and vent lines) connect thecylinder 144 to a steering proportional valve 160. Hydraulic lines 162,164 connect the steering proportional valve 160 to respective blockingvalves 166, 168. Hydraulic line 170 connects the steering proportionalvalve 160 to a steering pump 172. Hydraulic line 174 connects thesteering proportional valve 160 to hydraulic line 176, which connects totank 178, and hydraulic line 176 connects the blocking valves 166, 168to a tank 178. The hydraulic lines can be actuated to extend or retractthe cylinder 144. Extension or retraction of the cylinder 144 results inpivoting of the caster 122 at the upright shaft 150, allowing forsteering of the caster 122. The steering control system 130 therebyprovides for single wheel rear axle steering of the windrower 100.

FIG. 6 is a top view of the steering control system 130 in a left turnoperation. Arrow 180 represents the direction of rotation of the caster122 as actuated by the steering assembly 134. In the left turnoperation, the steering assembly 134 is hydraulically controlled toretract the cylinder 144. FIG. 7 is a top view of the steering controlsystem 130 in a right turn operation. Arrow 182 represents the directionof rotation of the caster 122 as actuated by the steering assembly 134.In the right turn operation, the steering assembly 134 is hydraulicallycontrolled to extend the cylinder 144. In both left and right turnoperations, steering of the windrower 100 is controlled by a combinationof the front wheel dual-path steering and the left-hand side rear wheelsteering assembly 134, while the right-hand side wheel passively castersto follow the control of steering with the damping assembly 132providing passive damping during castering.

The exemplary steering control system 130 therefore provides for activesteering control to one of the two rear wheels on the windrower 100,while the other rear wheel remains passively castering during the rearaxle steering mode. Steering of one of the rear wheels, particularlyduring high-speed operation, provides additional stability to the frontdrive dual-path steering system rather than providing primary steeringcontrol. Thus, rather than providing the primary steering control of thewindrower 100, steering of one of the rear wheels assists in stabilizingthe system overall during high-speed and normal operation modes of thewindrower 100.

As compared to conventional windrowers, the windrower 100 includes asteering cylinder 144 coupled to one of the casters 120, 122 that allowsfor directional control of the caster 120, 122, while the other caster120, 122 maintains a traditional shimmy damper configuration withoutactive steering control. The cylinder 144 uses the sensor 152 (e.g.,internal cylinder position sensor, external position sensor, radialpotentiometer, proximity sensor, or the like) to determine and transmitthe radial position of the caster 122 to a controller. A control valvemanifold can be used to extend and retract the steering cylinder 144. Asteering pump 172 can be used to provide pressure/flow to the manifold,and valves and lines can provide a path for flow to return to tank 178during field operation. An electronic steering wheel/device positionsensor can be used to provide operator commanded steering wheel/deviceposition to the controller, with such data used by the controller tocalculate and execute the commanded steering position (e.g., extensionor retraction of the cylinder 144) via a control algorithm.

The windrower 100 can remain in front drive dual-path steering duringthe different operation modes of the windrower 100, with the rearsteering acting to supplement or assist in stabilizing operation of thewindrower 100. In some embodiments, steering in the field can beprovided only by the front drive dual-path steering, while the rear axlesteering can function along with the dual-path steering duringhigh-speed (e.g., road) operation mode. As noted above, the steeringcylinder 144 connects to an arm 146 attached to the top of the uprightshaft 150 (e.g., a caster vertical pivot shaft) at one end and the rearaxle 124 (via the flange 148) at the opposing end.

The rod and barrel ports of the cylinder 144 can be plumbed to theproportional steering valve 160. The hydraulic lines to the steeringcylinder 144 have blocking valves 166, 168 to tank 178 that are normallyopen, allowing free flow of fluid into and out of the cylinder 144during field operation. Blocking valves 166, 168 are provided to blockflow back to tank 178 in the rear axle steering mode. When all blockingvalves 166, 168 are blocking flow back to tank 178, the movement of thesteering cylinder 144 can be controlled by the steering valve 160.

In the field/free castering operation mode, all blocking valves 166, 168are actuated into the open position, allowing free flow of fluid intoand out of the steering cylinder 144. The steering cylinder 144 isextended and retracted based on the caster 122 position due to steeringcontrol from the front drive wheels. The steering valve 160 remains inthe centered or closed position during this operation. The steeringcylinder 144 acts as a caster damper during the field operation mode asthe flow of fluid into and out of the cylinder 144 provides a viscousdamping force on the steered caster 122. The non-steered caster 120receives damping force from the passive shimmy damper 136 during fieldoperation.

In the rear axle steering operation, the operator selects rear axlesteering operation through the operator console in the cab or anothercommand switch (e.g., at a user interface). The operator can be promptedto drive straight forward in order to orient the steered caster 122 andrear wheel 128 behind the rear axle 124 as this is this orientation ofthe caster 122 during rear axle steering operation. In some embodiments,a proximity sensor 153 can be incorporated into the steering assembly134 to detect and transmit data to the controller regarding the positionof the caster 122 and/or wheel 128 relative to the rear axle 124 (seeFIG. 4). In some embodiments, a similar proximity sensor can be disposedon the caster 120 to detect and transmit data to the controllerregarding the position of the caster 122 and/or wheel 126 relative tothe rear axle 124. For example, a magnetic sensor on the caster 122 anda fixed target on the rear axle 124 can be used to sense when the caster122 is in a position behind the rear axle 124 prior to initiating therear axle steering operation.

FIG. 8 is a detailed view of the steering assembly 134. As noted above,in some embodiments, a proximity sensor 121 can be rigidly coupled tothe axle 124 via the casing for the shaft 150. In some embodiments, thesensor 121 can be disposed within an opening of a flange extending fromthe casing for the shaft 150. A target 123 can be rigidly coupled to thecaster 122. The target 123 can rotate with rotation of the caster 122with the sensor 121 detecting the target 123 only when the caster 122has rotated behind the axle 124. Upon detection of the target 123 withthe sensor 121, the rear axle steering operation can be initiated.

When the controller receives data from the sensor 152 that the steeringcylinder 144 is in the steering straight position, the blocking valves166, 168 can be actuated to shift and block all flow into and out of thesteering cylinder 144. Blocking flow into and out of the steeringcylinder 144 creates a closed circuit where the retraction and extensionof the steering cylinder 144 (and thereby the steering direction of thesteered caster 122) is controlled by the steering valve 160. To steerthe rear wheel 128, the operator can input a steering command by turningthe steering wheel/device to a desired position. A steering sensorreceives data corresponding with the steering command (e.g., the amountof rotation of the steering wheel, the input desired rotation of thewindrower 100, or the like). In some embodiments, the steering sensorcan be electronically coupled to the steering wheel/device. Thecontroller uses the position data received from the steering sensor tocommand a steering angle of the rear axle steering cylinder 144 withposition sensing. Thus, the controller can extend or retract thesteering cylinder 144 as needed to achieve the desired input at thesteering wheel/device, with the sensor 152 detecting and transmittingthe position of the steering cylinder 144 (and thereby the caster 122)to the controller.

FIG. 9 is a static image of a hydraulic circuit 200 of the steeringcontrol system 130. The hydraulic circuit 200 includes a relief valve202, a steering pump 204, a steering wheel or device position sensor206, and a controller 208. The hydraulic circuit 200 includes a tank210, a return to tank blocking valve 212, a return to tank blockingvalve 218, and a steering proportional directional valve 220. Thehydraulic circuit 200 includes a steering cylinder 216 and a cylinderposition sensor 214.

FIG. 10 is the hydraulic circuit 200 in an in-field operation mode. Theblocking valves 212, 218 are opened, allowing free flow of hydraulicfluid into and out of the steering cylinder 216 and back to tank 210.Steering of the windrower 100 is controlled by the front drive wheeldual-path steering system only (e.g., without steering from the cylinder216).

FIG. 11 is the hydraulic circuit 200 in a straight path operation mode.The steering proportional directional valve 220 is centered with thesteering cylinder 216 centered (e.g., partially extended). Steering ofthe windrower 100 is controlled by a combination of the front drivewheel dual-path steering and the rear axle steering from the cylinder216. The desired steering position can be provided to the controller 208by a steering wheel or device position sensor 206, while the actual rearwheel position feedback can be provided to the controller 208 by thesteering cylinder position sensor 214 (e.g., on the left-hand sidecaster as shown in FIGS. 1-6).

FIG. 12 is the hydraulic circuit 200 in a right turn operation mode. Thesteering proportional directional valve 220 is shifted to extend thesteering cylinder 216, resulting in the windrower 100 turning right.Steering of the windrower 100 is controlled by a combination of thefront drive wheel dual-path steering and the rear axle steering from thecylinder 216. The desired steering position can be provided to thecontroller 208 by a steering wheel or device position sensor 206, whilethe actual rear wheel position feedback can be provided to thecontroller 208 by the steering cylinder position sensor 214 (e.g., onthe left-hand side caster as shown in FIGS. 1-6).

FIG. 13 is the hydraulic circuit 200 in a left turn operation mode. Thesteering proportional directional valve 220 is shifted to retract thesteering cylinder 216, resulting in the windrower 100 turning left.Steering of the windrower 100 is controlled by a combination of thefront drive wheel dual-path steering and the rear axle steering from thecylinder 216. The desired steering position can be provided to thecontroller 208 by a steering wheel or device position sensor 206, whilethe actual rear wheel position feedback can be provided to thecontroller 208 by the steering cylinder position sensor 214 (e.g., onthe left-hand side caster as shown in FIGS. 1-6).

FIGS. 14-16 are perspective and detailed views of an exemplary steeringcontrol system 300 of the present disclosure. The steering controlsystem 300 can be substantially similar in structure and function to thesteering control system 130 except for the distinctions noted herein.Therefore, like reference numbers refer to like structures.Particularly, rather than having a steering assembly associated withonly one caster, the steering control system 300 includes a steeringassembly associated with each of the casters with only one of thesteering assemblies being actuated to steer the rear wheels and theother steering assembly moving in an equal and opposite direction fromthe first steering assembly.

The steering assembly 134 on one of the casters 122 includes the sensor152 in communication with the controller 154 such that the detectedposition of the caster 122 (based on the extension/retraction of thecylinder 144) can be used to control the cylinder 144 to achieve thedesired steering of the windrower 100. Rather than a passive damper, thesteering control system 300 includes a second steering assembly 302 atthe other caster 120. The steering assembly 302 includes a steeringcylinder 304 capable of being hydraulically actuated to extend orretract, thereby adjusting the rotational position of the caster 120.

Rather than having a sensor associated with the steering cylinder 304,the steering assembly 302 can be hydraulically coupled to the steeringassembly 134 such that actuation of the steering cylinder 144 to extendor retract automatically actuates the steering cylinder 304 to extend orretract in an equal and opposite direction. The extension or retractionof the steering cylinder 304 is therefore directly tied to actuation ofthe steering cylinder 144 and is dependent on the single sensor 152 ofthe steering control system 300. Both steering cylinders 144, 304 areactuated to steer the casters 120, 122, with the position of only one ofthe casters 120, 122 being measured by the sensor 152 (e.g., amaster/slave arrangement with the steering cylinder 144 acting as themaster component and the steering cylinder 304 acting as the slavecomponent).

Each of the steering cylinders 144, 304 is coupled to the steeringproportional valve 160 via hydraulic lines 306, 308. The steeringcylinders 144, 304 are coupled to each other by a hydraulic line 310,which is further coupled to a blocking valve 312 by a hydraulic line314. The steering proportional valve 160 is coupled to blocking valves316, 318 by hydraulic lines 320, 322. Each of the blocking valves 312,316, 318 is coupled to tank 178 by a hydraulic line 176, and thesteering proportional valve 160 is coupled to tank 178 by a hydraulicline 324. The steering proportional valve 160 is further coupled to thesteering pump 172 by hydraulic line 170.

FIG. 17 is a top view of the steering control system 300 in a left turnoperation. Arrow 180 represents the direction of rotation of the caster122 as actuated by the steering assembly 134, and the direction ofrotation of the caster 120 as actuated by the steering assembly 302 tiedto the steering assembly 134. In the left turn operation, the steeringassembly 134 is hydraulically controlled to retract the cylinder 144,and the cylinder 304 of the steering assembly 302 is hydraulicallycontrolled to extend in an equal and opposite direction to the cylinder144 due to fluid connection of the barrel ends of the cylinders 144,304. FIG. 18 is a top view of the steering control system 300 in a rightturn operation.

Arrow 182 represents the direction of rotation of the caster 122 asactuated by the steering assembly 134, and the direction of rotation ofthe caster 120 as actuated by the steering assembly 302 tied to thesteering assembly 134. In the right turn operation, the steeringassembly 134 is hydraulically controlled to extend the cylinder 144, andthe cylinder 304 of the steering assembly is hydraulically controlled toextend in an equal and opposite direction to the cylinder 144. In bothleft and right turn operations, steering of the windrower 100 iscontrolled by a combination of the front wheel dual-path steering andthe rear wheel steering assemblies 134, 302, with the right-hand sidesteering assembly 302 controlled based on the left-hand side positionsensor 152.

The steering control system 300 therefore provides for rear axlesteering of the windrower 100 with cylinders 144, 304 hydraulicallycoupled to move in equal and opposite directions during operation withthe position of only one cylinder 144 measured to control the steeringaction of the rear wheels. The steering control system 300 is capable ofproviding stability to the windrower 100 during high-speed operationwith directional control of the rear wheels without necessitatingmultiple position sensing cylinders 144, 304. As noted above, thewindrower 100 includes two steering cylinders 144, 304 for eachrespective caster 120, 122. Only one of the cylinders 144 includes ameans for the controller 154 to determine the radial position of thecaster 122 (e.g., an internal cylinder position sensor, an externalposition sensor, a radial potentiometer, or the like).

A control valve manifold can be used to extend and retract the steeringcylinders 144, 304. A steering pump 172 can provide pressure or flow tothe manifold, and valves and lines can provide a path for flow to returnto tank 178. An electronic steering wheel/device position sensor can beused to provide an operator commanded steering wheel/device position tothe controller 154 which, in turn, can be used to calculate and executethe commanded steering position via a control algorithm (e.g., theamount of extension or retraction of the cylinder 144, 304).

The windrower 100 can retain the front drive dual-path steering for alloperations, with the steering control system 300 assisting instabilizing operation of the windrower 100 in at least the high-speedoperation mode. For example, steering in the field can be provided onlyby the front drive dual-path steering, while the rear axle steeringfunctions along with the dual-path steering during high-speed road modeoperation. The cylinders 144, 304 connect to respective arms 146, 138attached to the top of the caster vertical pivot shaft at one end andthe rear axle 124 of the windrower 100 at the other end (via flanges148, 140).

The barrel ports of the cylinders 144, 304 can be plumbed together,while the rod ports can be plumbed to the proportional steering valve160. The hydraulic lines to the steering cylinders 144, 304 includeblocking valves 312, 316, 318 to tank 178 that are normally open,allowing free flow of fluid into and out of the cylinders 144, 304during field operation. The blocking valves 312, 316, 318 are providedto block flow back to tank 178 in the rear axle steering mode. When allblocking valves 312, 316, 318 are blocking flow back to tank 178,movement of the steering cylinders 144, 304 can be controlled by thesteering valve 160.

Such arrangement results in retraction of a first cylinder (e.g.,cylinder 144) causing fluid to be displaced from the barrel end of thefirst cylinder and into the barrel end of the second cylinder (e.g.,cylinder 304). The fluid displacement actuates the second cylinder toextend an equal amount that the first cylinder retracts when theproportional valve 160 shifts to retract the first cylinder. The setupallows a position sensor 152 to be provided on only one steeringcylinder for providing steering cylinder position feedback to thecontroller 154.

In the field/free castering operation mode, all blocking valves 312,316, 318 are opened, allowing free flow of fluid to and from thesteering cylinders 144, 304. The steering cylinders 144, 304 extend andretract based on the caster 120, 122 position due to the steeringcontrol from the front drive wheels. The steering valve 160 remains inthe centered or closed position during such operation. The steeringcylinders 144, 304 act as caster dampers during field operation as theflow of fluid into and out of the cylinders 144, 304 provides a viscousdamping force.

In the rear axle steering operation mode, the operator can select therear axle steering operation through an operator console, user interfaceor other command switch. The operator can be prompted to drive thewindrower 100 straight forward in order to orient the casters/rearwheels behind the rear axle 124 as this is the orientation of thecasters 120, 122 during the rear axle steering operation. In someembodiments, one or more proximity sensors can be used to detect theposition of the casters 120, 122 relative to the rear axle 124. When thecontroller 154 receives data indicating that the sensing cylinder 144 isin the steering straight position, the blocking valves 312, 316, 318 canbe shifted to block all flow into and out of the steering cylinders 144,304, creating a closed circuit in which the retraction of a steeringcylinder on one side causes an equal and opposite extension of thesteering cylinder on the other side of the windrower 100.

To steer the rear wheels, the operator can make a steering input commandby turning the steering wheel or device to a desired position. Suchposition can be sensed by a steering sensor coupled to the steeringwheel or device. The controller 154 can use the detected position of thesteering wheel or device to command a steering angle of the rear axlesteering cylinder 144 with position sensing. For example, the controller154 can actuate the steering cylinder 144 to extend or retract toachieve the desired steering with the position sensor 152 providingfeedback to the controller 154 regarding actuation of the cylinder 144.

Because the cylinder 144 includes the position sensor 152 and thecylinder 304 does not, the controller 154 uses the position data fromthe position sensor 152 for adjustments of both cylinders 144, 304. Forexample, the cylinder 144 can be actuated to extend by shifting thesteering valve 160 to retract the cylinder 304. As a further example, ifthe input command necessitates that the cylinder 144 be retracted, thesteering valve 160 can shift to retract the cylinder 144 which, in turn,extends the cylinder 304 due to the barrel ports of the cylinders 144,304 being plumbed together. In some embodiments, the steering valve 160can hydraulically connect only to the rod ends of the steering cylinders144, 304 with no direct fluid communication with the barrel ends of thesteering cylinders 144, 304.

As such, the steering control system 300 allows for one position sensingcylinder 144 to determine the radial position of the caster 122, whilethe second caster 120 and cylinder 304 do not necessitate positionsensing. The steering valve 160 acts directly on only the rod end of thecylinder 144, reducing the flow requirement for a comparable system inwhich valves act on both the rod and barrel ends (e.g., due to thereduced volume of the rod end compared to the barrel end). It should beunderstood that the position sensing can be on either the cylinder 144or cylinder 304.

In some embodiments, the steering valve can act on the barrel end of thecylinders, the rod end port of the steering cylinders can be plumbedtogether rather than the barrel ends or the like. In some embodiments, aproximity sensor can be used on the non-position sensing side to confirmthat the non-sensing side is centered when entering the rear axlesteering operation. For example, a magnetic sensor and a fixed targetthat is sensed only when the caster is in the proper rear axle steeringstraight orientation can be used. Alternatively, an active calibrationcan take place to enter the rear axle steering mode by prompting theoperator to drive straight forward for a predetermined distance afterthe position sensing caster is in a straight orientation position. Atsuch point, all blocking valves can block flow from the steeringcylinders to tank and the system 300 can be a closed circuit with rearaxle steering active.

FIG. 19 is a static image of a hydraulic circuit 400 of the steeringcontrol system 300. The hydraulic circuit 400 includes a relief valve402, a steering pump 404, a steering wheel or device position sensor406, and a controller 408. The hydraulic circuit 400 includes a tank410, return to tank blocking valves 414, 420, 424, and a steeringproportional directional valve 422. The hydraulic circuit 400 includessteering cylinders 412, 418 and a cylinder position sensor 416associated with only the steering cylinder 418.

FIG. 20 is the hydraulic circuit 400 in an in-field operation mode. Theblocking valves 414, 420, 424 are opened, allowing free flow ofhydraulic fluid into and out of the steering cylinders 412, 418 and backto tank 410. Steering of the windrower 100 is controlled by the frontdrive wheel dual-path steering system only (e.g., without steering fromthe cylinders 412, 418).

FIG. 21 is the hydraulic circuit 400 in a straight path operation mode.The steering proportional directional valve 422 is centered with thesteering cylinders 412, 418 centered (e.g., partially extended).Steering of the windrower 100 is controlled by a combination of thefront drive wheel dual-path steering and the rear axle steering from thecylinder 418. The desired steering position can be provided to thecontroller 408 by a steering wheel or device position sensor 406, whilethe actual rear wheel position feedback can be provided to thecontroller 408 by the steering cylinder position sensor 416 (e.g., onthe left-hand side caster as shown in FIGS. 14-18).

FIG. 22 is the hydraulic circuit 400 in a right turn operation mode. Thesteering proportional directional valve 422 is shifted to retract thesteering cylinder 412 which, in turn, extends the steering cylinder 418,resulting in the windrower 100 turning right. Steering of the windrower100 is controlled by a combination of the front drive wheel dual-pathsteering and the rear axle steering from the cylinder 418. The desiredsteering position can be provided to the controller 408 by a steeringwheel or device position sensor 406, while the actual rear wheelposition feedback can be provided to the controller 408 by the steeringcylinder position sensor 416 (e.g., on the left-hand side caster asshown in FIGS. 14-18).

FIG. 23 is the hydraulic circuit 400 in a left turn operation mode. Thesteering proportional directional valve 422 is shifted to retract thesteering cylinder 418 which, in turn, extends the steering cylinder 412,resulting in the windrower 100 turning left. Steering of the windrower100 is controlled by a combination of the front drive wheel dual-pathsteering and the rear axle steering from the cylinder 418. The desiredsteering position can be provided to the controller 408 by a steeringwheel or device position sensor 406, while the actual rear wheelposition feedback can be provided to the controller 408 by the steeringcylinder position sensor 416 (e.g., on the left-hand side caster asshown in FIGS. 14-18).

FIG. 24 is a static image of an alternate hydraulic circuit 500 of thesteering control system 130. The hydraulic circuit 500 includes a reliefvalve 502, a steering pump 504, and a tank 506. The hydraulic circuit500 includes a return to tank blocking valve 508, and a steeringproportional directional valve 510. The hydraulic circuit 500 includes asteering cylinder 512 and a cylinder position sensor 514.

While exemplary embodiments have been described herein, it is expresslynoted that these embodiments should not be construed as limiting, butrather that additions and modifications to what is expressly describedherein also are included within the scope of the present disclosure.Moreover, it is to be understood that the features of the variousembodiments described herein are not mutually exclusive and can exist invarious combinations and permutations, even if such combinations orpermutations are not made express herein, without departing from thespirit and scope of the present disclosure.

The invention claimed is:
 1. A steering control system for a harvester,comprising: a first cylinder configured to be coupled to a rear axle ofthe harvester at one end and rigidly coupled to an upright shaft of afirst caster of the harvester at an opposing end; a sensor associatedwith the first cylinder and in communication with a controller, thesensor detecting a position of the first cylinder; and a damperconfigured for extension and retraction and to be coupled to the rearaxle of the harvester at one end and an upright shaft of a second casterof the harvester at an opposing end; wherein in a road operation mode,the first cylinder is actuated by the controller to extend or retract tocontrol steering of the first caster, and the sensor transmits data tothe controller regarding the detected position of the first cylinder;and wherein the damper is free of sensing and provides passive dampingto the second caster.
 2. The steering control system of claim 1, whereinone end of the first cylinder is configured to be coupled to the rearaxle of the harvester by a flange.
 3. The steering control system ofclaim 1, wherein the first cylinder is hydraulically plumbed to asteering proportional valve for actuation of the first cylinder toextend or retract.
 4. The steering control system of claim 3, whereinthe steering proportional valve is hydraulically plumbed to a rod endand a barrel end of the first cylinder.
 5. The steering control systemof claim 1, wherein the detected position of the first cylinder isrepresentative of a position of the first caster relative to the rearaxle of the harvester.
 6. The steering control system of claim 1,comprising a proximity sensor configured to detect a position of thefirst caster relative to the rear axle of the harvester.
 7. The steeringcontrol system of claim 1, wherein cantering of second caster isunaffected by actuation of the first cylinder to extend or retract. 8.The steering control system of claim 1, wherein the sensor is at leastone of an internal position sensor, an external position sensor, or apotentiometer.
 9. The steering control system of claim 1, wherein in afield operation mode, free flow of hydraulic fluid into and out of thefirst cylinder provides passive damping by the first cylinder to thefirst caster.
 10. A steering control system for a harvester, comprising:a first cylinder configured to be coupled to a rear axle of theharvester at one end and rigidly coupled to an upright shaft of a firstcaster of the harvester at an opposing end; a sensor associated with thefirst cylinder and in communication with a controller, the sensordetecting a position of the first cylinder; and a second cylinderconfigured to be coupled to the rear axle of the harvester at one endand an upright shaft of a second caster of the harvester at an opposingend; wherein in a road operation mode, the first cylinder is actuated bythe controller to extend or retract to control steering of the firstcaster, and the sensor transmits data to the controller regarding thedetected position of the first cylinder; and wherein the second cylinderis free of sensing and is hydraulically coupled to the first cylinder tomove in an equal and opposite direction of the first cylinder to controlsteering of the second caster.
 11. The steering control system of claim10, wherein barrel ports of the first and second cylinders arehydraulically coupled together, and rod ports of the first and secondcylinders are hydraulically coupled to a steering proportional valve.12. The steering control system of claim 11, actuation of the firstcylinder to retract displaces fluid from a barrel end of the firstcylinder into a barrel end of the second cylinder.
 13. The steeringcontrol system of claim 12, wherein displacement of the fluid into thebarrel end of the second cylinder actuates the second cylinder to extendin an equal magnitude to retraction of the first cylinder.
 14. Thesteering control system of claim 10, wherein the detected position ofthe first cylinder is representative of a position of the first andsecond casters relative to the rear axle of the harvester.
 15. Thesteering control system of claim 10, comprising a proximity sensorconfigured to detect a position of the first caster or second casterrelative to the rear axle of the harvester.
 16. The steering controlsystem of claim 10, wherein the sensor is at least one of an internalposition sensor, an external position sensor, or a potentiometer. 17.The steering control system of claim 10, wherein in a field operationmode, free flow of hydraulic fluid into and out of the first and secondcylinders provides passive damping by the first cylinder to the firstcaster and the second cylinder to the second caster.
 18. A harvester,comprising: a frame; at least one front axle comprising first and secondfront wheels pivotally mounted to the front axle; at least one rear axlecomprising first and second casters pivotally mounted to the rear axle;and a steering control system comprising: a first cylinder coupled tothe rear axle at one end and rigidly coupled to an upright shaft of thefirst caster at an opposing end; a sensor associated with the firstcylinder and in communication with a controller, the sensor detecting aposition of the first cylinder; and a damper configured for extensionand retraction and coupled to the rear axle at one end and an uprightshaft of the second caster at an opposing end; wherein in a roadoperation mode, the first cylinder is actuated by the controller toextend or retract to control steering of the first caster, and thesensor transmits data to the controller regarding the detected positionof the first cylinder; and wherein the damper is free of sensing andprovides passive damping to the second caster.
 19. The harvester ofclaim 18, wherein castering of second caster is unaffected by actuationof the first cylinder to extend or retract.
 20. A harvester, comprising:a frame; at least one front axle comprising first and second frontwheels pivotally mounted to the front axle; at least one rear axlecomprising first and second casters pivotally mounted to the rear axle;and a steering control system comprising: a first cylinder coupled tothe rear axle at one end and rigidly coupled to an upright shaft of thefirst caster at an opposing end; a sensor associated with the firstcylinder and in communication with a controller, the sensor detecting aposition of the first cylinder; and a second cylinder coupled to therear axle at one end and an upright shaft of the second caster at anopposing end; wherein in a road operation mode, the first cylinder isactuated by the controller to extend or retract to control steering ofthe first caster, and the sensor transmits data to the controllerregarding the detected position of the first cylinder; and wherein thesecond cylinder is free of sensing and is hydraulically coupled to thefirst cylinder to move in an equal and opposite direction of the firstcylinder to control steering of the second caster.